Microbial Fuel Cell and Method of Use

ABSTRACT

A microbial fuel cell comprising a cathode module, an anode module, a means for feeding source water to the anode module, and a means for feeling air to the source water after said anode module, wherein the source water is introduced in the anode module and discharged at the cathode module, a membrane is not used to transfer electrons, and the source water does not flow through a layer between the cathode and anode modules, such as glass wool or beads.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of the earlier filing date of U.S.Provisional Application No. 61/058,667, filed Jun. 4, 2008, which isincorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to an improved membrane-less andbarrier-free microbial fuel cell for treating nutrient containing sourcewater, such as wastewater.

The present invention is based on the technology of using a microbialfuel cell that converts chemical energy into electrical energy throughthe metabolism of microorganisms, in which the chemical energy is in theform of organic substances present in wastewater.

BACKGROUND

A microbial fuel cell or biological fuel cell is a bio-electrochemicalsystem that drives a current by mimicking bacterial interactions foundin nature. Micro-organisms catabolize compounds such as glucose,acetate, butyrate or wastewater and can generate electrons with sourcestreams carrying catabolizable compounds, including those identifiedabove. The electrons gained from this oxidation are transferred to ananode, where they depart through an electrical circuit before reachingthe cathode. Here they are transferred to a high potential electronacceptor such as oxygen. As current flows over a potential difference,power is generated directly from biofuel by the catalytic activity ofbacteria.

The microbial fuel cell is a device that converts chemical energy toelectrical energy by the catalytic reaction of microorganisms. A typicalmicrobial fuel cell consists of anode and cathode modules separated by acation specific membrane. In the anode module, fuel is oxidized bymicroorganisms, generating electrons and protons. In typical microbialfuel cells, electrons are transferred to the cathode module through anexternal electric circuit, and the protons are transferred to thecathode module through the membrane. Electrons and protons are consumedin the cathode module, combining with oxygen to form water.

Most of the microbial cells are electrochemically inactive. The electrontransfer from microbial cells to the electrode is facilitated bymediators such as thionine, methyl viologen, methyl blue, humic acid,neutral red and so on. Most of the mediators available are expensive andtoxic. Some microbial fuel cells do not require a mediator but useelectrochemically active bacteria to transfer electrons to the electrode(electrons are carried directly from the bacterial respiratory enzyme tothe electrode). Among the electrochemically active bacteria are,Shewanella putrefaciens, Aeromonas hydrophila, and others. Bacteria insuch MFCs typically have electrochemically-active redox enzymes such ascytochromes on their outer membrane that can transfer electrons toexternal materials.

When micro-organisms consume nutrients in source water in aerobicconditions they produce carbon dioxide and water. However when oxygen isnot present they produce carbon dioxide, protons and electrons. Onereaction that may occur is as follows:

C₁₂H₂₂O₁₁+13H₂O --->12CO₂+48H⁺+48e ⁻

In fact, all biodegradable materials, such as proteins, fats and lipids,among others, are broken down to reaction products in the degradationprocess. These materials are all potential sources of energy through thepresent invention.

In order to generate a useful current it is necessary to create acomplete circuit, not just shuttle electrons to a single point.

Microbial fuel cells (“MFC”) have a number of potential uses. The firstand most obvious is harvesting the electricity produced for a powersource. Virtually any organic material could be used to ‘feed’ the fuelcell. Water used in various applications, such as food manufacturing andagriculture, create polluted waste streams. The organic matter from suchstreams can be used to feed the fuel cell. Manufacturers are required byregulation to clean such waste streams and current solutions have highcapital costs, high operating costs, large spatial footprints, and largecarbon footprints. Microbial fuel cells, such as the MFC describedherein, could be installed to treat effluent from a number of processesthat generate or discharge an effluent with a sufficient BOD, such aswaste water treatment plants. The bacteria consumes nutrients from thewater and produce power. The use of microbial fuel cells is a very cleanand efficient method of energy production.

Since the power generated from a microbial fuel cell is directlyproportional to the nutrient content of the source. The nutrient contentof source water may be evaluated as biochemical oxygen demand (“BOD”)values. A microbial fuel cell BOD sensor can be used to measure realtime BOD values. An additional preferable benefit of a microbial fuelcell is the reduction of BOD from the influent to the effluent. Suchmeasurements may indicate the efficacy of a cell.

In a microbial fuel cell, oxygen and nitrate are preferred electronacceptors and act through reduction of oxygen and nitrate to generatecurrent. Most microorganisms have an outer cellular structure whichshows strong non-conductivity. The typical microbial fuel cells thecathode module and the anode module are separated from each other with amembrane and current generation occurs in the anode module and acation-exchange membrane is used to transfer protons from the anodemodule to the cathode module. In other microbial fuel cells a barrier isused and limitations have been found in the distance from the anode tothe cathode.

The present inventors have also found that naturally occurringmicroorganisms found in source water streams, such as nutrient richeffluent streams (i.e., with sufficient BOD levels), can directlytransfer electrons previously generated from oxidation of organicsubstances in an anode module and can be naturally cultured during theoperation of a biofuel cell.

In previously developed microbial fuel cells, where the cathode moduleand anode module have been separated from each other, the generation andtransfer of electrons and protons by means of bio-reaction in an anodemodule and the consumption of electrons and protons occurs by means ofthe following reaction:

4e+4H⁺+O²⁻→2H₂O

Typically, a circuit is formed across a membrane for operating microbialfuel cells for source water treatment in a continuous manner.

Thus, in the typical microbial fuel cell, a cation-exchange membrane hasbeen used to transfer protons from the anode module to the cathodemodule. If microorganisms in an anode module are sufficiently culturedduring the process, electrons and protons are generated from theoxidation of water nutrients, such as glucose or cellulose. Generatedprotons may be transferred via a cation-exchange membrane whileelectrons are transferred through an external electric coupling. In thecathode module the electrons and protons are consumed in a reductionprocess involving oxygen or nitrogen. In combination, the oxidationprocess in the anode and the reduction process in the cathode creates apotential difference and a current may be drawn through an externalelectrical coupling. Cation-exchange membranes, however, are subject tofouling, which reduces the efficiency of cation transfer across acation-exchange membrane. Moreover, because the anode module is a closedchamber, fouling can cause a pH decrease in the anode module which coulddetrimentally affect the micro-organisms or require the use of a buffersolution. In addition to fouling problems, membranes are very expensiveand introduce cost issues, particularly at higher throughputs.

As an alternative to the use of a membrane, US Published App. No.20050208343 teaches using glass wool or glass beads as a barrier betweenthe cathode and the anode. However, this negatively impacts thescalability of the microbial fuel cell and fouling will still impactperformance of the microbial fuel cell. The published application alsolimits the distance between the anode and cathode, likely due to the useof such barriers. Such distance issues are overcome in the embodimentsdescribed herein which overcome these limitations and disadvantages, andthe impact of these problems with a barrier free microbial fuel cellthat uses flow to prevent backflow of oxygen to the cathode chamber.

SUMMARY

The embodiments described herein relate to a microbial fuel cell thatovercomes the limitations and disadvantages described above by providinga membrane and barrier-free microbial fuel cell which lowers capitalcosts, cleans wastewater, and converts wastewater treatment into energy.In a preferred embodiment, the microbial fuel cell has an anode modulecontaining an anode, a cathode module containing a cathode, and a sourcestream that contains sufficient nutrients to enable microorganisms inthe source stream to grow a biofilm on fill that is contained in theanode module. Unlike typical membrane-using microbial fuel cells, theprotons flow with the source stream to the cathode, where oxygen isintroduced to the stream to produce an aerobic reaction. The flowprevents oxygen diffusion into the cathode chamber which maintains theanaerobic environment in the anode chamber. Optionally, a flowrestrictor or backflow preventer may be used. In one embodiment, a flowrestrictor may be used. In another embodiment a one-way valve may beused. In another embodiment, a unidirectional pump may be used.

A preferred embodiment described herein is to an improved barrier-free,membrane-free microbial fuel cell, which can be operated without using acation-exchange membrane or any barrier between the cathode and theanode modules, such as glass wool or glass beads. The microbial fuelcell described herein allows for continuous flow, prevents foulingissues, and promotes scalability to fit the particular application. Amembrane-less and barrier-free microbial fuel cell according to apreferred embodiment is an improved device capable of being utilized ina process of treating nutrient containing source water, such as foodprocessing effluent or wastewater (sewage) with electricity generation.

As described above, the microbial fuel cell and other technologydescribed herein is characterized by improving a microbial fuel cell toenable it to treat nutrient containing source stream, as measured by BODlevels, with a membrane-less and barrier-free microbial fuel cellcomprising a cathode module, an anode module, a means for feeding air tothe cathode module, and a means for feeding source stream to the anodemodule.

Further, a membrane-less and barrier-free microbial fuel cell of thepresent invention is based on a novel and unique concept of firstanaerobically treating the nutrient containing source water in an anodemodule and then aerobically treating the source stream from the anodemodule in a cathode module.

The membrane-less and barrier-free microbial fuel cell according to apreferred embodiment further does not require a particular distancebetween a cathode module and an anode module, and preferably uses aconductive, non-biocidal material, such as graphite as an electrode inthe anode module and silver, silver coated, copper, copper coated, or alike conductive contact with biocidal or antibiotic properties as anelectrode in the cathode module.

In another preferred embodiment, the fill that is used as the electrodein the anode module is derived from using a graphite foil that iswrapped around a neutral core rod, such as PVC. The graphite foil usesspacers to create gaps in each wrapped layer to allow the source streamto flow between each wrapped layer. The spacers can be configured toprovide an optimal flow path for the source stream to maximize surfacecontact time with the electrode. In the cathode module the preferredfill is a conductive foil, most preferably with biocidal or antibioticproperties, such as silver. The silver coated foil is similarly wrappedusing spacers to create a flow path between each wrapped layer of silverfoil. The spacers may be smaller and the wrap may be tighter due to thewater quality in the cathode module compared with the anode, namely,there will be less chance of plugging due to biofouling. It may also bepreferably to arrange the spacers to achieve turbulent flowcharacteristics in the cathode module to inhibit biofilm formation.

Optionally, an alternative embodiment can use a buffer solution in ananode module in order to maintain the optimum pH for growth ofmicroorganisms in the presence of organic acids generated whenartificial wastewater is fed as a fuel so that the activity ofmicroorganisms distributed in the anode module is kept constant.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the aforementioned aspects of thepreferred embodiments as well as additional aspects and alternativeembodiments thereof, reference should be made to the DetailedDescription of Embodiments below, in conjunction with the followingdrawings.

FIG. 1 is a diagram illustrating an exemplary microbial fuel cell inaccordance with one embodiment of the microbial fuel cell describedherein.

FIG. 2 illustrates how the MFCs described in the specification addressesmanufacturing effluent and energy issues.

FIG. 3 illustrates an scalable module of a preferred embodiment.

FIG. 4 illustrates a depiction of a membrane using MFC.

FIG. 5 illustrates the scalability of the present invention through theaddition of modules.

FIG. 6 depicts a rod and foil fill used in the anode and cathodemodules.

FIG. 7 depicts a rod and foil fill used in the anode and cathodemodules.

DETAILED DESCRIPTION OF EMBODIMENTS

Membrane and barrier-free microbial fuel cells and methods of use aredescribed herein. Reference will be made to certain embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. While the invention will be described in conjunction with theembodiments, it will be understood that it is not intended to limit theinvention to these particular embodiments alone. On the contrary, theinvention is intended to cover alternatives, modifications andequivalents that are within the spirit and scope of the invention asdefined by the appended claims.

Moreover, in the following description, specific details are set forthto provide a thorough understanding of the described embodiments.However, it will be apparent to one of ordinary skill in the art thatalternative embodiments may be practiced without these particulardetails. In other instances, methods, procedures, and components thatare well-known to those of ordinary skill in the art are not describedin detail to avoid obscuring aspects of the present embodiments of theinventions.

FIG. 1 is a diagram illustrating an exemplary membrane and barrier-freemicrobial fuel cell of the present invention. There is an anode 1, whichhas an anode inlet 2, an anode outlet 3, and fill 4. The fill can be,for example, spherical plastic beads coated in carbon ink, graphiteparticles—regular or irregular, or a graphite foil (or sheet). Otherconductive, non-toxic materials may be used. Where graphite foils (atleast 1 per module) are used, the rod (such as a PVC or metal rod,preferably not a material detrimental to the system by contributingtoxicity to the system—noncylindrical rod shapes may be used, such asrectangular) may be 0.1″ but preferably greater than 0.5″, such as about1″ diameter (a greater diameter may be used based on the applicationwith concomitant loss of surface area) with a spacer or stackingmaterial attached to the graphite foil intended to cause a channel withpreferably some tortuous path to mix the liquid and which willpreferably flow through in a serpentine path through the rolls of thefoil formed around the rod, increasing the contact surface and slowingthe relative flow, which will promote biofilm growth. The foil may berolled any number of times to practically fit in the module but therolls should be designed to substantially fill the anode module space,allowing for even flow of the source water via the void space throughthe channels. A distributor may be used to distribute the source streamto evenly flow across the diameter of the anode module.

One suitable graphite foil is Pyro-Tex Joint Sealant from Slade, Inc.,Statesville, N.C., which is 0.015″ thick and 40″ wide. The stackingmaterial may be attached in a perpendicular orientation relative to thedirection of rolling but may be varied to optimize mixing and/or thebiofilm thickness and should be sufficiently raised to permit sufficientflow of the source water and biofilm growth. The stacking material isflexible in a preferred application or may be of fixed semi-circularshape to permit rolling. The preferred final shape of the stackingmaterial after rolling is adaptable to suit the application and may besemi-circular or semi-elliptical in nature such that a fluid pathway isformed for the source water to flow through. The goal is to design thebaffling such that the source water is exposed to the greatest surfacearea while avoiding flow preventing obstructions. One suitable stackingmaterial is Buna-N cord stock, such as the quad cross-section shape,which can be obtained from McMaster-Carr Supply Company.

In the cathode module, the fill can be, for example, spherical beads ofa catalytic metal or metal coated material (such as silver, palladium,platinum, rhodium, copper) or a catalytic metal coated film, forexample, silver, palladium, platinum, rhodium, or copper. The preferredcoating is silver. Other coatings that are conductive and have somebiocidal or antibiotic quality may preferably be used. Although notpreferred, other conductive metal coatings may be used that do not havea biocidal or antibiotic quality. Such coating may be modified withcatalytic surface active compounds. One suitable foil can be obtainedfrom Techni-Met of Windsor, Conn., 3 mil SKC Skyrol SH31 substratecoated with 800 Angstroms Ag and is 40″ wide. More preferably, the foilis coated on both sides. Air or some other oxygen containing gascontacts the charged source stream in the cathode module. The stackingmaterial may also be less raised due to the lack of or significantlylesser biofilm (any such biofilm would be incidental and not preferred)in the cathode module, allowing for greater surface contact.

The microbial fuel cell of FIG. 1 has an anode module 16 and a cathodemodule 17. From both the anode and cathode module are the electricalcontacts, anode 10 and cathode 11. The anode contact (e.g., foil, bead,wire, electrical tape) needs to not be toxic to the microbes and may becoated with a non-toxic material or be made of a conductive, non-toxicmaterial. The cathode contact may be of any conductive material. Theenergy generated is collected at an energy management or collectiondevice 12. The nutrient containing source stream 13 enters the anodemodule through the anode inlet 2 and flows over the distribution screen18. Microbes culture in the anode module on the fill (not shown) andproduce energy consuming BOD content of the source stream. The electroncontaining stream exits the anode module at the anode output and istransferred to the cathode module via the transfer tube 15. Optionally,a flow restrictor 6 may be used to prevent backflow of oxygen to theanode module. Alternatively, a one way valve or a number of otherbackflow prevention approaches may be used. The electron containingstream enters the cathode module, where it contacts a distributor 18.The stream is oxygenated for aerobic treatment in the cathode module.The cathode module preferably contains conductive spherical fill but maybe other shapes that allow flow through the module and preferably limitschanneling. More preferably the fill is a conductive foil rolled usingstacking material, as described above. A most preferred conductive foilwill also have biocidal or antibiotic properties and be corrosionresistant, such as silver. Alternatively, where spherical or othershaped bead or particle fill is used, baffles may be used in the moduleitself to help prevent channeling in both or either the anode or cathodemodule. Oxygen or air or some other suitable gas mixture (e.g., ozone)with sufficient oxygen is added or sparged into the flow to the cathodemodule and may be added upstream of the cathode inlet 7 but after theflow restrictor or backflow preventer 6 at addition point 9 and/or maybe added within the cathode, preferably upstream of the distributor atpoint 5. The cleaned source water 14 exits the cathode module at thecathode outlet 8.

In a preferred embodiment of the microbial fuel cell described above,the microbial fuel cell of FIG. 1 may use a film-based fill in either orboth the anode module and cathode module. FIG. 6 depicts such a filmrolled fill 600, which uses a foil or sheet 601 that is rolled on a rod602 with prearranged and attached baffles 603, which can be designed tocreate a preferable flow and surface contact area. FIG. 7 depicts analternate film rolled fill 700 with an alternative baffle design, wherethe baffles 703 on the foil 701 are closer together and designed suchthat when rolled on rod 702, the feedwater or source stream flow 704 ismore likely to cause turbulent and tortuous flow, increasing the contactsurface area. FIGS. 6 and 7 are depicted prior to rolling the film intoa cylindrical rod with a diameter substantially similar to the anode orcathode module within which it will be inserted. The source stream willflow across the rod, through the rolled layers where the source streamwill exit the module as effluent 705.

Another embodiment is a membrane and barrier-free MFC that is flexiblyscaled to the needed size by adding additional modules. FIG. 3 depictsan embodiment of such a module 30 where the size may be about one cubicmeter (or about 158.5 gallons), for example, and such modules containingan anode module 32 and a cathode module 34, separated by a physicalbarrier 33 but where the effluent from the anode module 31 a is theinfluent for the cathode module. Such modules may be configured to workin parallel and/or in series, depending on the target output goals ofthe particular user. A source stream, such as a wastewater effluent 31,at a flow rate of 100 gallons/hr, for example, could produce acontinuous electrical power output of 5 kW, recovered by electricalconnections to the anode 36 and cathode 37, which is then connected 39to a means to recover the electric potential across the anode andcathode 38. By configuring the modules in parallel, the user couldsignificantly reduce the COD/BOD in the effluent stream 35 to the leveldesired by the user. If a cleaner effluent is needed, the modules may beconfigured in series for example. Where such a configuration is used,the user may take advantage of knowing the quality of the subsequenteffluent streams to configure the fill to optimize surface area topromote growth, energy production, and BOD reduction.

FIG. 5 depicts a representation of a collection of such modules 30 inboth series and parallel as a bank of MFC modules 500 that areconfigured to receive source stream 501 into an influent distributorbank 502. The cleaned effluent streams collect in an effluentdistributor bank 504 to discharge the cleaned effluent 503. Thecollective energy generated is captured by a means 512 for use.

Alternatively, hydrogen can be recovered in another embodiment, in whichoxygen would not be added to the cathode module and an electricalpotential would be supplied to the system to effect the reaction.

Source streams of a sufficient BOD concentration, for example greaterthan 50 ppm, alternatively greater than 150 ppm, alternatively greaterthan 300 ppm, greater than 500 ppm, more preferably greater than 1000ppm is introduced into the anode module of the microbial fuel cell anddischarged at a portion of the cathode module after passing through theanode module and transferred to the cathode module. Optionally, thesource stream passes through a flow restrictor, unidirectional pump, ora backflow preventer. The source stream may be sampled or otherwisemonitored at some point after the anode module to measure the BOD and/orCOD to determine the treatment efficiency regarding organic substances.The quantity of electric charge is calculated by integrating theelectric current generated over time. The result is analyzed forcorrelation to organic substances removed from the cell, in order todetermine electricity generation efficiency. The flow may be adjusted orother adjustments may be made in response to maintain and/or optimizethe system.

According to a preferred embodiment, it is important that oxygen issufficiently fed to a cathode module since oxygen supply is arate-controlling factor. It has been found that air contains sufficientoxygen, though in some applications, it may be preferable to feed ahigher concentration of oxygen to ensure optimal operation.

According to a preferred embodiment, the electrode used in a cathodemodule may be made of or coated with conductive, biocidal materials,such as copper, silver, or platinum. Silver has been used as a preferredmaterial.

According to a preferred embodiment, a device having a type representedin FIG. 1 is used to treat source water continuously. Source water maybe kept in a reservoir and may be introduced into an upper portion ofthe anode module, either through pumping or gravity flow. Alternatively,the source water may be introduced into a lower portion of the anodemodule of the microbial fuel cell by means of a flow control pump. Whilesource water is flowing through the anode module, organic substancespresent in the source water are anaerobically digested bymicroorganisms, thus resulting in the generation of electrons. Theseelectrons are transferred to the anode and protons are transferred tothe cathode through aerobic reaction, without passing through anexternal barrier such as glass wool or beads. Under the premise that themaximum transfer rate to the cathode module is equal to thedecomposition rate of the aforesaid organic substances in the anodemodule, sufficient air is fed to the cathode module to ensure themaximum potential is achieved.

A microbial fuel cell according to the present invention can be operatedwithout using an expensive cation-exchange membrane or similar glasswool or glass bead barrier or interface between the cathode and anodewith an expectation of greater efficiency by limiting fouling. Moreover,a membrane-less microbial fuel cell of the present invention has furtheradvantages in that source stream primarily treated in an anode modulecan be used as an electrolyte in a cathode module. Therefore, a specialelectrolyte does not necessarily have to be utilized in the cathodemodule. In addition, the source water is aerobically treated in thecathode module or where hydrogen is sought, air or oxygen is not addedto the cathode module.

In an alternative embodiment particulate fill in the anode module may bestratified by size with a larger size where the source water firstenters the module to increase interstitial spacing for flow purposes andmay decrease by gradients to the outlet of the anode module.

Where the embodiment uses a foil module fill, the baffling or channelingcan be customized and designed to the application. For example, a highsolids source stream or a source stream containing large particles mayutilize a larger baffle to allow more space between rolls. The bafflingmay also be more spread out to prevent plugging of channels. Moreover,it has been found that such baffling offers an unexpected advantage overfill materials such as beads or felt, where flow characteristics may becontrolled. For example, in the cathode module, turbulent flowcharacteristics may be preferable while in the anode module,non-turbulent flow is preferable.

The following examples are presented to provide a more detailedunderstanding of the invention. They are for illustrative purposes onlyand are not to be taken as limitative.

Example 1

In determining the BOD reduction efficacy, a sample of dairy effluentwater (feedwater) was taken at T1 at the point of entry into the anodeof the microbial fuel cell. At time T2 a second sample was taken at theeffluent of the cathode of the microbial fuel cell, where T2−T1=theresidence time of the microbial fuel cell. The biochemical oxygen demandof the source steam was measured to be 2470 mg/l and the biochemicaloxygen demand of the effluent from the microbial fuel cell was measuredto be 1400 mg/l. A 43.3% BOD reduction was realized by treatment of thesource stream by a membrane-free, barrier-free microbial fuel cellcorresponding to an embodiment of the microbial fuel cell described inthis specification using a graphite foil in the anode and asilver-coated foil in the cathode. The silver-coated foil was 3 mil SKCSkyrol SH31 substrate coated with 800 Angstroms Ag and the graphite foilin the anode was 0.015″ thick Pyro-Tex Joint Sealant from Slade, Inc.The surface area of the graphite foil was 14 ft². The volume of theanode module was 3.293 liters. The flow was continuous at a rate of107.99 ml/min The residence time in the anode module was 30.49 minutes.The surface area of the silver-coated foil in the cathode module was 35ft². The volume of the cathode module was 6.170 liters. The flow ratewas 107.99 ml/min and the residence time in the cathode module was 57.14minutes. A flow pump was used, such continuous flow prevented backflowof oxygen from the cathode to the anode.

Example 2

Dairy wastewater was fed from a 275 gallon tank as a source stream at arate of 4 ml/min, generating a voltage of up to 1.13V over a period ofabout 10 days, previously a voltage of up to about 18V was recorded.During the 10 day period mentioned above, the average voltage recordedthrough a Keithley 614 electrometer was 0.63V, with a low voltage of0.51V. The fill used in the anode was a rolled graphite foil and in thecathode ¼″ propylene balls coated with Creative Materials #124-46 silverconductive ink were used. The air flow at times was 120 ml/min Theresults show that microorganisms in an anode module have the capacity togenerate and carry an electric charge to the cathode and an electriccharge can be generated across the anode and cathode.

The concepts and embodiments disclosed herein can be applied over abroad scope of industries and with a variety of source streams. Examplesof preferred feedwater streams are from food and beverage processing,agriculture, wood and pulp processing, and municipal wastewatertreatment. More specific examples include dairies, poultry, pig farms,cattle farms, fruit and vegetable processors, corn ethanol production,pet food producers, sugar product producers, and the like. The generalapproach described herein can be used to treat anoxic waters, or deadzone water regions. Conceptually, FIG. 2 is a depiction of benefits of aMFC. The wastewater from a manufacturing plant 21 could also be anynutrient rich feedwater, that flows into a MFC 31, producing cleanerwater 41 and electricity or hydrogen 51.

It is not difficult to see that the simplicity of the design allows forscalability without worry of membrane issues, as found in membrane usingMFCs. FIG. 4 is a depiction of a membrane MFC, where 404 is the membraneconnecting the anode chamber 416 and the cathode chamber 417. A biofilmdeposits on the anode 401 under anaerobic conditions and the microbesconsuming the nutrients in the feedwater 413 generate energy and theeffluent 403 will typically exhibit a reduced BOD/COD. The cathode 402operates under aerobic conditions with both water and air entering 408and exiting 407 the cathode chamber. The potential is created over acation-exchange membrane 404, which is subject to limitations such asfouling and introduces significant costs. A means 412 is used to thencapture the energy potential across the membrane through connections tothe anode 410 and cathode 411. With each module, a distinct membrane isrequired and each membrane is subject to failure and fouling, makingscalability undesirable due to the maintenance issues and costs. Byeliminating the membrane in the embodiments described herein, thedisadvantages and problems with using a membrane are eliminated.

While the preferred embodiments have been described herein, variationsand modifications within the scope of what would be known to one ofskill in the art are possible without deviating from the broadprinciples of the invention, for example, a biocidal treatment zone,such as an ozone and/or ultraviolet light zone, may be added to theembodiments to further treat the effluent water.

1-10. (canceled)
 11. A membrane-less and barrier-less microbial fuelcell comprising a cathode module, an anode module, a means for feedingsource water from the anode module to the cathode module, and a meansfor introducing oxygen into said cathode module.
 12. The fuel cell ofclaim 2, wherein said fuel cell has an inlet configured to feed sourcewater continuously.
 13. The fuel cell of claim 2, wherein two or morefuel cells are used in conjunction with said source water.
 14. The fuelcell of claim 4, wherein said fuel cells are in parallel.
 15. The fuelcell of claim 4, wherein said fuel cells are in series.
 16. The fuelcell of claim 2, wherein a means of supplying a potential is formedacross the anode and cathode modules.
 17. The fuel cell of claim 2,wherein the anode module comprises a fill at least partially comprisinggraphite.
 18. The fuel cell of claim 2, wherein the cathode modulecomprises a fill at least partially comprising silver.
 19. The microbialfuel cell of claim 18, wherein the cathode module comprises a fill,wherein the fill used in the cathode module comprises at least onerolled silver foil and where both the anode and cathode rolled foil fillfurther comprises stacking material attached to at least one side ofboth said foils.